Treatment of cellulosic materials



Feb 5, 1946- J. D. POLLARD TREATMENT 0F CELLULOSIC MATERIALS Filed April 30, 1943 INVENTOR L/O/V/V p0 AD,

fn/#WM ATTORNEY l Patented Feb. s, 1946 TREATMENT CELLULOSIC MATERIALS Joln;n D. Pollard, Stamford, Conn'., assigner to erican Cyanamid Company, New N. Y., a corporation of Maine York,

Application April 30, 1943,- Serial No. 485,215

7 Claims.

This invention relates to improvements in nonflbrous cellulosic iilms and the like. More particularly, it relates to the treatment of nonbrous cellulosic bodies in sheet, tube or illament form with aminotriazinealdehyde condensation products whereby subsequently applied coating compositions are anchored more firmly thereto. The invention includes the treated cellulosic body and the process by which it is made.

Although non-librous, transparent iilms have many outstanding properties and have enjoyed wide-spread use as wrapping material etc., it is well-known by those in the art that conventional untreated cellulosic iilms, particularly of regenerated cellulose, possess poor water resisting characteristics. Regenerated cellulose products, and even some of the cellulose esters and ethers now on the market in 111m form, have unreacted hydroxyl groups which are hydrophilic in character. As a result, these products absorb water readily when in contact with moist bodies and become swollen and weak. It has also been found that water vapor readily passes through thin films of these materials making them relatively inleiective in preventing loss of moisture from the product wrapped with them.

Attempts have been made to improve the water 'repellent characteristics and impermeability of cellulosic wrapping material by treatment with y water repellent waxes, aluminum soaps, and the like, usually incorporated in a nlm-forming substance which is applied to the cellulosic body.

more ilrmly to the cellulosic illm. These anchoring treatments have, however, generally neces- Cellulosic sheets thus treated retain their transparency and other advantageous properties and have greatly improved water repellency and impermeability. However, when these treated sheets remain in prolonged contact with water; as is the case'when they are used to wrap moist foods such as fish, meat, butter, cheese, vegetables, etc., water penetrates the top-coating, the cellulosic material swells, and the water repellent lm is loosened and sloughs oil.. Unless special steps are taken to bond the water repellent coating to the cellulosic sheet failure of the bond between the two may occur within a Iew minutes after immersion of the coated cellulosic sheet in water. Obviously, the utility of such cellulosic sheets is greatly reduced by the inability o! the water repellent coating to remain firmly attached to its cellulosic base under adverse conditions.

To correct the difficulties caused by separation of the water repellent coating composition from the cellulosic nlm, it has been proposed to treat' the cellulosic lm with a bonding material intended to anchor the water repellent coating sitated the use of organic solvents in their application. The initial cost o! the solvent, the necessity of special equipment for its application, the dangers and the inconvenience of its use, and other disadvantages are, of course, apparent. Some of the anchoring agents proposed have also been relatively expensive. Furthermore, of conslderable importance is the fact that some types of anchoring materials are of limited effectiveness and will not prevent loosening of the water repellent coating upon prolonged contact with water. SomeV anchoring materials also fail to anchor some types of nlm-forming coating compositions to cellulosic bodies. My invention avoids all of these difficulties by employing an anchoring composition which can be applied from `aqueous solution and at the same time rmly anchor all types .oi' film-forming coating compositions to cellulosic bodies.

Cellulosic films used as wrapping materials, masking tape, adhesive tape, etc., are also commonly coated with pressure and/or heat sensitive adhesive compositions. Although the adhesive qualities of the seating composition to itself or to some other body may be adequate, if it will not firmly adhere to its cellulosic base it is quite obvious that its value as a sealing agent is greatly diminished. Accordingly, it is frequently desirable that the sealing composition be made to adhere more firmly to its cellulosic base. It is one of the advantages of my invention that nlm-forming adhesives can be made to adhere more 'ilrmly to a cellulosic film when the illm has been treated with aminotriazine-aldehyde condensation-products of the kind and Vtype to be hereinafter disclosed.

Frequently letters and designs are printed-on cellulosic sheets. Although the sheets and printing need not be water repellent, it is nevertheless desirable that the printing material stay on its base sheet if accidently placed in contact with water. It is another advantage o1' my invention that printed matter, when the printing ink contains film-forming matter of the type hereinafter disclosed, can be made to adhere more firmly to cellulosic sheets when the latter are treated lwith aminotriazine-aldehyde condensation products in accordance with4 my invention.

From the foregoing it will be seen that, broadly speaking, the principal-object of my invention is to improve non-brous cellulosic products particularly of the type commonly used as wrapping material. Another object of my invention is to provide a treated cellulosic sheet which can be coated with a film-forming substance whereby the latter is firmly anchored to its cellulosic base and is resistant to the loosening effects of water. Another object of my invention is to provide. a sheet of water repellent regenerated cellulose of improved water resistance. Other objects of .my invention are to provide a simple, inexpensive and practical method of applying an anchoring composition to cellulosic films which requires no special equipment or material changes in conventionalprocesses 'of preparing cellulosic films. Still other objects of my invention will appear from what has been previously said and from what appears hereinafter.

'I'he aforesaid objects of my invention are attained by treating non-fibrous cellulosic sheets, films, pellicles, tubing, filaments, etc., oi regenerated cellulose, cellulose esters and cellulose ethers with aqueous solutions of aminotriazinealdehyde condensation products, particularly those having hydrophilic, cationic properties. The

cellulosic films to be treated may be of regenerated cellulose prepared from solutions of cellulose xanthate, cuproammonium cellulose.' cellulose acetate, cellulose nitrate, etc. The cellulosic films may also be of a cellulose ester or ether such as cellulose acetate, cellulose nitrate, ethyl cellulose, methyl cellulose or similar cellulosic material containing unreacted hydroxyl groups and hence Y being hydrophilic in character. The treated cellulosic lbody may be freshly prepared and still wet or it may have been previously prepared, dried and stored. It may contain softeners, dyes, pigments, and other modifying agents or not.

'I'he aminotriazine aldehyde condensation products which I employ in my new process are, for the most part, known compounds. They are prepared by reacting an aldehyde; such as formaldehyde, acetaldehyde, propionoaldehyde, or other aliphatic aldehyde, as well as furfural, etc., with an aminotriazine containing one, two or three reactive amino groups; such as for example, melamine, ammeline, ammelide, formoguanamine, acetoguanamine, propionoguanamine, 4-meth3'1- 2 acetoguanamine, etc. These condensation products are prepared by heating 1 mole of the aminotriazine with from 2 to l0 moles of the aldehyde, preferably, in an alkaline medium. Preparation of typical aminotriazines will be illustrated in the specific examples. Aminotriazine-aldehyde condensation products suitable for use in my process may alsobe prepared by other methods which need not be described here.

For reasons of economy and because of their greater effectiveness, I prefer to use those aminotriazine-aldehyde condensation products prepared by the reaction of melamine with .aldehydes and particularly with formaldehyde. The condensation product preferred is a methylol melamine, containing approximately 3.3 moles of formaldehyde combined with l mole of melamine. Other condensation products containing from 2 to 6 moles of formaldehyde per mole of melamine are also suitable forv use in my invention. These f condensation products are unpolymerized or only thus treated possesses some advantages over an untreated cellulosic film, the treatment by no means provides the benefits obtainable by the use of certain aqueous solutions containing cationically active, hydrophilic, partially polymerized melamine.- formaldehyde particles. Solutions containing the melamine-formaldehyde material in this particular form are obtained by dissolvpartially polymerized; that is, they are uncured.

They are soluble in water, with heating if necessary. or soluble in dilute solutions of strong acids.

Although regenerated cellulose films can .be treated with freshly prepared aqueous solutions of melamine-formaldehyde condensation prod-- ucts, the anchoring eifect obtained by such treatment is not particularly good as will be seen from the specic examples. While a cellulosic iilm To prepare aqueous solutions of methylol mel- Y amine having these particular properties, I dissolve a substantially uncured methylol melamine condensation product having from 2 to 6 moles of combined aldehyde per mole of melamine in an aqueous solution of an acid. As acids, I may use strong mineral or organic acids such as hydrochloric, sulfurous, phosphoric, acetic, formic, and the like. The amount of methylol melamine to be dissolved may vary from about 0.1 to 4.0 moles of acid per mole of methylol melamine. In most cases the pH of the solution is above 0.5 but below 3.0 and always less than 4.0. The amount of acid depends 4somewhat upon the concentration of the resinous solution. For example, in a solution containing 12% of methylol melamine, I may use from about 0.7 to 1.4 moles of hydrochloric acid per mole of methylol melamine. As the concentration of the methylol-melamine in the aqueous solution is decreased, I may use a lower molecular proportion of acid. Thus, for example, in an aqueous solution containing 3% of methylol-melamine, an amount of acid corresponding to about 0.4 mole per mole of methylol-melamine has resulted in the formation of aged solutions satisfactory for use in my process.

After the methylol-melamine has been dissolved in the acid solution, it is allowed to age until the methylol melamine has acquired certain properties which have proven to be particularly desirable in treating cellulosic films. The aging period varies with a number of factors and it is not possible to give the exact aging period ior all conditions. At room temperatures at a resin concentration of 12% and a molecular methylolmelamine-acid ratio of 1:1, the aging period may be from 24 to 48 hours. At reuxing temperature the aging may be reduced to 4 or 5 hours. Again, at room temperatures using a methylol-melamine-acid ratio of 1:0.8 the aging period may vary from 5 to 24 hours for optimum results. 0i course, if the solution is used before it has reached its optimum aging period, for example after 2 hours, it will nevertheless give greatly improved results over those solutions which have not been aged at all.

lDuring the aging period certain important changes take place. 'I'he methylol-melamine which may originally have been substantially monomeric in character is believed to become partially polymerized. As the resinous particles become larger in size their presence is indicated by the formation of a bluish haze in the solution. When a beam of light is passed through these aged solutions, the well-known Tyndall eiect may be observed. Although, I have not been able to see these particles by means of ordinary optical miscroscopes, it has been shown that .colloidal solutions of particles of approximately 0.1 micron in diameter exhibit haziness. It would appear, therefore, that the size oi.' the partially polymerized methylol-melamine particles does not exceed 0.1 to 1.0 micron in diameter.

` sulting crystals.

A l asume Another important distinguishing characteristic of the methyloi melamine particles in the aged solution is their cationic activity. When an aged acid solution of a methylol-melamine condensation product is placed in an electrophoresis cell and direct current applied, the resinous particles, whether the solution exhibits haziness or not, migrate to the cathode. This would indicate that they are positively charged. Whether or not this characteristic influences their action on regenerated cellulose is not known at the present time but it has been observed that cellulose has a negative charge and that the aged methylol-melamine particles in the solutions appear to be preferentially adsorbed by the cellulosic film. It has also been observed ,that solutions of methylol-melamine polymers which are not cationic in character do not give the same results that the cationic methylol-melamine polymers do.

Another characteristic of the aged methylolmelamine particles is that they are hydrophilic in character. 'I'he acidic methylol-melamine solutions can be diluted with water to concentrations aslow as l/2% of methylol-melamine without causing precipitation ofthe methylol-melamine particles from solution. This is important in that I can age the acidic methylol-melamine solutions until they have optimum properties and then dilute them to very low concentrations in which condition they can be stored for weeks without undergoing substantial change. The dilute solutions also enables me to impregnate cellulosic lms with very small amounts of the condensation product.

A simple test which indicates that the formation of partially polymerized cationic methylolmelamine particles has taken place and that the solution is suitable for use consists merely in the addition of concentrated hydrochloric acid to a small amount of the aged solution. If a precipitate is obtainedy the presence of small amounts of partially polymerized cationic resin is indicated. An unaged solution will not respond to the test.

The preparation of aged solutions of specific aminotriazine-aldehyde .condensation products and the treatment of cellulosic illms therewith will now be described in greater particularity by means of the following specific examples. It should be understood however, that these examples are given principally by way of illustration and are not to be construed as limiting my invention to the particular conditions described therein. All parts are by weight unless otherwise indicated.

` EXAMPLE' 1 Aqueous solutions of cationic acid-type aminotriazine-aldehyde condensation products suitable by heating these reactants, at a pH of 9.0 for minutes, cooling, separating and drying the re- To prepare the cationic resin solution 50 parts by weight of the crystals are dissolved in a solution of 27.6 parts of commercial 18 B. hydrochloric acid and 125 parts of water ages a bluish haze develops yand the colloidal solution exhibits the well-known Tyndall eiiect when a beam of light is passed through it. The

formation of the haze and the presence of the Tyndall eifect indicates that the diameters of at least some of the resinous particles suspended in this solution are approaching the range of 0.1 to 1.0 micron. When a samplevoi' the solution is placed in an electrophoresis cell and a direct current passed therethrough, the resinous particles migrate towards the cathode thus proving them to be cationic in character. Further aging of the resinsolution results in the formation of a dispersible gel which soon becomes undispersible and worthless for purposes of my invention.

Cationic acid-type aminotriazine-aldehyde resins suitable for use in treating regenerated cellulose lm can also be prepared by dissolving nonacid-type uncured aminotriazine resins in strong acids. amine-formaldehyde resin prepared under alkaline conditions using 1 mole of melamine and 3.35 moles of formaldehyde is boiled with 5 times its weight of water until dissolved. After cooling, an approximately equimolecular quantity of hydrochloric acid is added to the solution.v Upon standing at room temperature for several days, the solution develops a characteristic bluish haze indicative of the formation of colloidal resinous particles of ultra-microscopic size in the solution. These particles are cationically charged as evidenced by their migration to the cathode in an electrophoretic cell.

Aqueous solutions of cationic aminotriazine resins may also be prepared by reacting an aldehyde, such as formaldehyde, with a melamine salt or by condensing the melamine and aldehyde in the presence of free acid. Thus, for example, 20 parts by weight of melamine (1A mole) is mixed with 42 parts of 37% aqueous formaldehyde solution (1/2 mole) and diluted with about 160 parts of water. V6 mole of hydrochloric acid is then added together with sulcient water to dilute the mixture to a total of 420 parts by weight. The mixture is then heated at 40-50 C. for 1% to 21/2 hours, or until a clear solution is obtained. Upon aging this solution 24 to 48 hours at room temperature, or for a shorter time at elevated temperatures, resinous particles are formed therein having cationic properties. This solution may be diluted to 10% resin solids or less and kept at room temperature'for several weeks without appreciable change in the colloidal condition of the resin.

A mixture of l mole of ammeline, 6 moles of 32% aqueous formaldehyde solution and 3 moles of HaP04 was heated for 5 minutes at 90 C. with the addition of suilcient water to bring the nai solutionto 40% solids. The resulting ammelineformaldehyde resin contained approximately 3.2

with heating at F. until the condensation" product is dissolved. The solution is then diluted to about 14% solids and allowed to age at room temperatures for 24 to 48 hours. As the solution moles of combined formaldehyde and the pH of the solution (glass electrode) was 0.9. Upon aging forV 24 hours at room temperature the solution developed a bluish colloidal haze, which grew stronger and deeper until a dispersible vgel was formed after 'I days standing. Upon electrophoresls ofthe one-day old colloidalvsolution between platinum electrodes the resin exhibited a definite positive chargeas shown by its migration to the cathode.

A second ammeline resin was prepared by reiiuxing 1 mole of ammeline, 10 moles of aqueous formaldehyde solution and 0.8 moles of sulfuric acid at 50% solids for 2.5 hours under atmospheric Thus, for example, a water soluble mel-f pressure. The resulting resin solution had a pH of-0.9 and remained clear for one week. After aging forone day it was tested by electrophoresis and found to be positively charged. A'

` A mixture of 1 mole 0f acetoguanamine, 3 moles of aqueous formaldehyde solution and 1 mole of HCl was reiiuxed at 48% solids for 1.5 hours at atmospheric pressures. The resulting solution had a glass electrode pH of 0.9, contained `approximately 2.5 moles of combined formaldehyde and was stable for one week at room temperature. After aging for one day it showed a positive charge when subjected to electrophoresis.

A partially polymerized, water insoluble spray dried trimethylol-melamine condensation product, which is available on'the market, may be dissolved in water with approximately equimolecular amounts of hydrochloric acid and allowed to age at room temperatures at a solids content of from to 50% for a period of from 1 or 2 hours up to a week or more'to yield a solu- I tion containing positively-charged, hydrophilic, partially polymerized methylol-melamine condensation products. These aged colloidal solutions are particularly useful in treating cellulosic lms in kaccordance with the teachings of my invention.

EXAMPLE 2 A quantity of sodium cellulose xanthate solution (viscose) was prepared in standard manner and allowed to ripen to a. stage suitable for platecasting lms. Using a glass rod viscose was applied to a glass plate and the plate with its coating was immersed in a sodium sulfate-sulfuric 25 grams of dry, powdered substantially unpolymerized methylol-melamine, containing approximately 3.35 moles of formaldehyde per mole of melamine, were dissolved in a heated solution (13o-140 F.) of 10.4 ml. of 20% B. hydrochloric acid in 100 ml. of water. The clear solution was then diluted to 204 ml. with water and allowed to age at room temperature for 24 hours. It was then diluted to a solids content of 3%. Glycerol, to serve as softener for the film, was added to the aged acid-resin solution in amounts of 8% and the solution was then ready for use. It was designated as solution Number 2.

Two more solutions of aged methylol-melamine-hydrochloric acid were prepared as just described. To one solution was added 0.0048% of maleic anhydride and to the other was added 0.0096% maleic anhydride. These solutions were numbered 3 and 4 respectively and were used in the tests to be described. Another aged acid solution of methylol-melamine was diluted to 3% methylol-melamine on a solids basis, mixed with an equal weight of polyvinyl alcohol and then diluted to 2% total solids (1% methylol-melamine and 1% polyvinyl alcohol). Eight per cent by weight of glycerol was added to the resin solution as before. This solution and the film treated with it were designated as Number 5.

methylol-melamine condensation product was dissolved in a heatedl solution gf 18 grams of glacial acetic acidin ml. of water. The clear solution was diluted to 204 ml. with water and allowed to age for 24 hours. It was then diluted to 3% solids, 8% by weight of glycerol added thereto and designated as Number 6 for use in the anchoring tests. A similar solution of the aged methylol-melamine-acetic resin was prepared and 0.0096% of maleic anhydride added ther'to. This solution was designated as Number l Sheets of the wet gel regenerated cellulose were immersed in the aged resin solutions for 5 mlnutes, removed to a flat metal plate and the excess resin solution squeezed off with a rubber window cleaner. Excess film was trimmed off the edges of the metal plate and the latter tted into a frame, arranged so that the edges of the nlm could be held firmly while drying. Frame, plate and lm were then placed in an oven at 200 F. for 8 minutes, allowed to cool, and the dried lm removed.

To test the ability of aged, cationic methylolmelamine solution's to anchor Water resistant Each of the sheets of regenerated cellulose treated with cationic4 methylol-melamine and numbered 2 to 7 and a sheet of the dried, untreated regenerated cellulose, numbered 1, to serve as a control were immersed in the above nitrocellulose solution and the excess film-forming composition removed by passing the films between glass rods separated by a distance calculated to yield, upon evaporation of the solvent, a moisture proof top coat of desirable thickness on both sides of the lm. The coated samples were then dried ln a circulating hot air oven for 2 minutes at 85-90 C. The samples were then trimmed to a size of approximately 3 by 4 inches to provide three freshly cut edges. 'I'he seven lmswere then immersed in water at room temperature (22 to 24 C.) and examined periodically to determine whether or not the water resisting coating was firmly anchored to its base sheet. 'I'he results of this series of tests are shown in the following table.

In this table, and also in the other tables, the designation O. K. means that the water resistant coating was firmly and completely anchored at all points to its cellulosic base. The designation Bl. indicates that blisters had appeared in the lm. It is pointed out that the formation of blisters is due to some extent to defects in the coating arising from the diiculty of obtaining perfect application of coating material, particularly by the ,hand methods used in these tests. In commercially produced sheets the formation of these blisters would not occur to such a great extent. The important consideration is, therefore, the determination of anchorage failure by separation and sloughing of the water resistant film, particularly at the out edges. Sloughing of the film was determined by squeezing the lm 25 grams of a substantially unpolymerized 75 between the thumb and forenger with a heavy plates, the edges securely clamped down,v and asaaooo that the blisters are large or many in number. 5

Results of this series of tests are as follows:

acetic acid and also containing 8% of glycerol was used to impregnate sheet Number 10.

Another resin solution, used to treat sheet Number 11, contained 8% glycerol, 1% of HClaged methylol-melamine and 1% polyvinyl alcohol.

Table I Condition i topcoat after immersion (or- Film 1 hr. 3 hrs. 8 hrs. 24 hrs. 72 hrs. 6 days 9 days 13 days Sep. at Bad sep... Coating oil.. 0. 0. K.. O. K.. Loose at cut edges. O. O. K.. S. Bl.. Do. 0. O. K O. K.. L. Bl. but no loose coating. 0. 0. K O. K.. O. K.

g. O K 0 Bl., loose at cut edges.

As will be seen from these results, the water resistant nitrocellulose coating commenced to separate from its untreated base sheet within an hour after immersion in water. On the other hand, the water resistant coating remained firmly attached to those viscose sheets which had been treated with aged cationic methylol-melamine solutions for a period of days.

EXAMPLE 3 dried in an oven for 6 minutes at 90-95 C. After cooling, the resin treated sheets were cut to convenient test sizes and impregnated with a dried this sheet was found to contain 1.4% of A sheet of the regenerated cellulose was treated with a 3% solution of HCl-aged methylolmelamine resin, removed from the resin solution, thoroughly washed with running water and then treated with an 8% solution of glycerol. When methylol-melamine resin based on the dry weight of the sheet. This sheet was designated Number 12.

Three more solutions of aged cationic methylol-melamine resin were prepared similar to the solution used to treat Number 9. However, additional amounts of glycerol were added tothe sheets so that they contained 10%, 12% and 15% of glycerol and 3% of methylol-melamine. These sheets were numbered 13, 14 and l5 respectively.

After treatment with the water resistant nitrocellulose lacquer described above, and dried for 2 minutes at 8590 C. the test sheets were immersed in water at room temperatures and examined periodically for failure of the top coat. The results of this series of observations are shown in the following table. l

Table II Condition of topcost after immersion fon- Film 8 hrs.

24 hrs. 3 days 8 days 12 days Coat sloughed... O. K

L. Bl. but no slough.

Do. Coat sloughed. L. B11). but no Slough.

nitrocellulose coating composition similar to that described in the preceding example.

The various test sheetsused in this series of experiments were treated with anchoring solutions'as follows. Number 8, to serve as control, was ltreated in an aqueous solution containing 8% glycerol. Sheet Number 9 was treated with a 3% aqueous solution of a methylol-melamine condensation product which had aged for 24 hours with an equimolecular proportion of HC1. The solution also contained 8% of glycerol as softener. After the sheet had been impregnated with the resin solution, it was found to have 2.8% of resin, dry basis, in it. Another aged methylolmelamine solution containing 3% of methylolmelamine aged for 24 hours at a solids content of 12% with an equimolecular proportion of 'I'hese results show that aged cationic methylol-melamine-acid-type condensation products can also be successfully used to bond film-forming coating compositions to regenerated cellulose a which has been prepared and dried by conven- Sheet Number EXAMPLE 4 The series of experiments described in Example 3 were repeated with the difference that an ethyl cellulose film-forming composition was applied to the resin treated regenerated cellulose coating composition was as follows.

, Dibutyl phthalate sheet. AThe composition of this water resistant Parts by weight Ethyl cellulose (med. viso.) 24.0 Parailln wax (M. P. 60 C.) 1.4 Sulfonated castor oil Lfty Dibutyl phthalate 6.6 Toluene l 193.4 Ethyl alcohol 50.0

Sheets of the resin treated regenerated cellulose were dried at 90-95 C. then impregnated with the above coating composition, and dried. They were then trimmed to expose uncoated edges and aged with an equimolecular proportion' of acetic acid at a concentration of 12% for 24 hours. Film 24 had a treatment with a solution containing 8% glycerol, 1% of aged methylol-melamine-I-ICI polymer and 1% of polyvinyl alcohol. Film 25 was treated with' an aged 3% methylol-melamine- HC1 resin, washed thoroughly with Water and then impregnated with an 8% glycerol solution prior to treatment with the chlorinated rubber immersed in water at room temperature. This coating composition. The results of the tests series of test sheets was numbered 16 to 20 inare shownin the following table.

Table IV I Condition oi topcoat after immersion for- Fum 1hr. 8l1rs. 24hrs. Bdays days 12 days 21 SloughI "st bot Badi slou heded es.` Coat ott W'sloughatbottom.. "peelallcutedges.. Same Same--.. Samo-... Same.

clusive. Number 16 was a control impregnated with an 8% glycerol solution. Sample Number Cationic methylol melamine polymers are shown to be highly effective in anchoring chlo- 17 was impregnated with a 3% aged methyloll30 rinated rubber topcoats to cellulosic lm.

melamine-HC1 solution. Sheet 18 was impregnated with an aged 3% methylol-melamineacetic acid solution. Sheet 19 was impregnated with a solution containing 1% of the aged methylol-melamine resin and 1% polyvinyl alco- 35 constituent Was prepared as follows:

sheet contained 1.4% resin on dry basis. The -results of this series of tests were as follows.

EXAMPLE 6 vA hlm-forming coating composition containing Pliolite (cyclicized rubber) as the film-forming Sheets of regenerated cellulose were impregnated with aqueous solutions of aged, cationic, partially Table III Condition of topcoat aiter immersion for- Fllm l l hr. 8 hrs.'A :i l" 24 hrs. 3 days 6 days 12 days Sep. at eut edge..-. Coating 011....

O. 0. K S. Bl S: B1 L. Bl Slight slough. O. K .v O. K O. K Bl Sloughed.

Slight slough Slight slough.. M slough at edges.. M slough at edges. Sloughed Slough at edges v .rin Coating of? f Although ethyl cellulose is a diillcult top coat to .55 products as previously described. Sheet Number anchor, these results showthat cationic methylol melamine polymers are highly elective in anchoring it to its cellulosic base.

EXAMPLE 5 A nlm-forming coating composition having the following formulation was prepared.

Toluene 243.0

` Sheets of resin treated regenerated cellulose were impregnated with this coating composition and dried. They were then trimmed to expose uncoated edges and immersed in water at room temperature. The results of these tests are shown in the following table. Film Number 21 was a control which had been treated with an 8% aqueous solution of glycerol. Film 22 was impregfpolymerized methylol melamine condensation 26 served as a control and was impregnated with an 8% solution of glycerol prior to application of the top coat. Sheet Number 27 was impregnated with an aged methylol-melamine-HCI solution containing 3% resin solids. Sheet Number 28 was impregnated with an aqueous solution containing 3% of an aged methylol-melamine-acetic acid condensation product. Sheet 29 was impregnated with a solution containing 1% of aged methylol-melamine-HCI condensation product and 1% of polyvinyl alcohol. The bathsfused to treat sheets 27, 28 and 29 each contained 8% by weight of glycerol as softener for the regenerated cellulose. Sheet Number 30 was impregnated with an aged cationic methylo1-melamineHC1con densation product containing 3% of methylolmelamine. It was th'en thoroughly washed with water and then impregnated with an 8% solution of glycerol. Results of this series of tests are shown in the following table.

Film 23 had been im- Table V Condition o! topcoat after immersion lor- Film 1 hr. s hrs. 24 hrs. 3 days days l2 days 2o Vbslight peel at Coating otl..

t 0. K. O. K. 0. K. 0. K.

Sheet Number 30 shows particularly well the fact vthat the resin treated cellulosic sheet can be washed with water to remove excess resin bemelamine polymer which had been aged for 24 hours at a solids content of 12% with an equi-V molecular proportion of HCl. After treatment in l5 fOre pplicatin 0f the 170D 008.12. the 3% resin solution, the sheets were thoroughly EXAMPLE? washed with running water and then impreg- A nhmmming coating composition cntam nated with a solution containing 8% by Weight ing a butyl methacrylate polymer as the essential of ammonium sulfamate and 2% glycerol' The film-forming material and containing paramn 20 Sheets were then dried and coated with the nitrowax as the water repellent constituent was pre c Cellulose the butyl methacl'ylate and the P110- pared having the following composition; lite coating compositions previously described. Parts by Weight After` drying, the sheets werey immersed in water polymerized butyl methacrylate 31 4 at room temperature and the anchoring effect paramn wax (M. P. 60 c.) 1,6 .25 of the cationic methylol-melamine observed. Toluene 243.0 The results are given in the following table.

Table VII Condition o! topcoat alter immersion forrum l hi'. 8 hrs. 24 hrs. 3 days I days Nu nui o. 'I "1 "1 Butryl".e motht::ry1ate.. 0. g-. Isig?. Isul?. llfmgh Puollw o. x.. o. K.. o. K o. K 0.1:.

A sheet of tinted regenerated cellulose, Number As will be seen, the aged methylol-melamine 32, was impregnated with an aqueous solution polymer does not lose its eil'ectiveness when the containing 8% glycerol and 3% of an aged 40 treated lmfis subjected to a washing treatment.

methylol-melamine-HCI polymer. Another sheet, Number 33, was impregnated with an aqueous solution containing 8% glycerol and 3% of aged methylol-melamine-acetic acid polymer. A third sheet, Number 34, of tinted regenerated cellulose 4 Table VI This observation was also made in the case of lms 12, 20, 25 and 30 previously described. The results also show that the methylol-melamine polymer is compatible wtih softeners other than glycerol and that the softener may be subsetilm after drying if desired.

Examen: 9

quently applied to the methylol-melamine treated 5 Three sheets of dried regenerated cellulose were impregnated for 5 minutes with an aqueous f solution containing 4% of glycerol, 4% of ura,..; and 3% of methylol-melamine polymer which 'l had been aged for 24 hours at a solids content of 12% with an equimolecular proportion of HC1. The treated cellulosic sheets were dried in an oven for 8 minutes at 200 F. and then coated on both sides with the nitrocellulosethe butyl methacrylate and the Pliolitel coating compositions previously described. After drying, the sheets were immersed in Water at room temtest but by far the greater proportion of the illm was anchored ilrmly to its cellulosic base after 6 days immersion in water. The initial sloughing may have been due to imperfections arising from coating technique.

EXAMPLE 10 .The anchoring emciency of cationic methylolmelamine polymers 'was compared with that of non-cationic melamine-formaldehyde and ureaformaldehyde condensation products. One anchoring bath contained 3% of a cationic methylolmelamine polymer which had been aged for 24 hours at a solids content of 12% with an equimolecular proportion of HCl. Another solution contained 3% of an aqueous solution of methylo1- melamine unaged and noncationic. An aqueous solution of a methylated methylol-melamine was also included in this group. Other aqueous baths were made up containing 3% of a urea-formaldehyde resin and 3% of a methylated ureaformaldehyde resin. Sheets of regenerated cellulose were impregnated in these baths for 5 minutes, then dried for 8 minutes at 200 F. and then coated on both sides with the nitrocellulose lacquer described above. The coated lms were dried for 2 minutes at 9095 C., trimmed to provide 3 freshly cut edges and then immersed in water at room temperature. The results of this series of tests are shown in the following table.

ated cellulose I is passed through a softening agent and cationic methylol-melamine polymer. Excess bath is removed by means of a suitable doctoring device such as rolls 3, or knives, air Jet, water spray, etc. (not shown). The impregnated iilm l is then dried 'by passing through a suitable drier 5 which may -be of the loft, tower. heated drum type or the like. In this drier the impregnated ilm is heated for a period of time ranging from 2 or 3 seconds to 20 minutes or more. at temperatures of about 60 to 150I C.. or higher, to cure the methylol-melamine to a substantially water insoluble stage. The dried and cured lm 8 may then be wound up andstored, or shipped, for further treatment or it may be directly treated, as shown, with a coating bath 1. The coating material may be applied, of course. by means of sprays, rolls, or other conventional type of coating apparatus (not shown) 'Ihe excess coating material is removed by means of a doctoring device 8. The coated film is then passed through a drier I0 to dry the coating composition. The nished product II may then be wound in` rolls and is ready for use. Since the coating or cellulosiclms and drying thereof is well known in the art, further discussion oil this part of the process is unnecessary.

'Ihe cellulosic lm I2 impregnated with the catonic methylol-melamine is illustrated in Fig. 2. So fas as I have been able to determine vthe methylol-melamine is uniformly dispersed throughout the cellulosic body. This is an important advantage of my invention since some of the previously described anchoring processes yield a sheet of cellulose with a lm of anchoring material on it as a separate body and under cer- Table IX Condition of topcoat alter immersion tor- Film 1hr. Shrs. 24hrs. adays days Control Coating on Aged methylol-melamlne O. K...- O. K 0. K... 0. K..- 0. K. Unaed methylol-melaminn 0. K Bad Slough Met ylated methylol-melamine Slough at bottom.. do Urea-formaldehyde. Slough at edge.. dn Methylated urea-formaldehyde. n do As will be seen methylol-melamine was the only material that gave any substantial anchoring effect to the nitrocellulose coating composition. While the unaged methylol-melamine polymer gave better results than any of the other polymers tested, it was much inferior to the aged cationic methylol-melamine polymer. The latter gave perfect anchorage for more than 6 days whereas the others al1 failed within eight hours.

In commercial production of cellulosic iilms using cationic methylol-melamine polymers in accordance with my invention the process will normally be substantially continuous. A typical anchoring and coating process may be exempliied by the accompanying drawing in which:

Figure 1 is a sectional elevation showing one- 'way of applying the cationic methylol-melamine polymer to regenerated cellulose film and thereafter applying a water-repellent coating;

Figure 2 is an isometric view of a section of the methylol-melamine impregnated cellulosic base sheet; and

Figure 3 is an isometric view showing the water repellent coating anchored to the regenerated cellulose base sheet.

In carrying out my invention, according to Fig. 1, a sheet of purified and washed gel regenertain conditions the anchoring lm may separate from its cellulosic base.

Figure 3 shows the cellulosic film I2 with top coats I3 and I4 ilrmly anchored thereto.

From the foregoing examples and discussion of my process, it will be evident that many modlcations may be made therein without departing from its fundamental principles. For example, the softening agent can be applied in a separate bath. Also, if desired the impregnated lm can be washed with water to remove excess methyolol-melamine. Instead of coating the treated film on both sides it may be coated on only one side, or, if desired, it may be treated in discontinuous areas as when printing designs or letters thereon. Also, it may 'be desirable to coat the treated nlm with adhesive compositions of known typ The amount of cationic methylol-melamine polymer incorporated in the sheet may vary from about 0.5 to 10%, or more, by weight. I'he amount of the polymer picked up by the sheet can be readily governed by controlling the concentration of the resin in the anchoring bath. I have used an anchoring bath containing about 3.0%

the impregnated sheet contained about 2.8% by :negoce weight of the ymetliylol-melainiue polymer. Us'- ing 1% of methylol-meiamine in the bath gave a sheet containing about l1%v of the polymer. Contrei of the amount or resin in the sheet may also be had by means of the doctoring device. l

Although no curing catalyst for the cationic methylol-melamine is generally necessary, my experiments have shown that the acid curing catalysts can be incorporated in the anchoring bath without impairing the anchoring eillciency of the methylol-melamine. I g

The methylol-melamine polymer is odorless, tasteless, non-poisonous, colorless, transparent, heat and light stable and accordingly is an ideal compound for use in the treatment ofcellulose films intended for wrapping foods.

'I'he methylol-melamine polymer is compatible with many different kinds of softeners, plasticizers, synthetic and natural resins, gums, cellulosic esters and ethers, rubber and rubber like materials, waxes. oils, dyes, pigments, etc. The water soluble or dispersible materials of this group may be incorporated in the aqueous methylolmelamine resin solution if desired.

The cationic methylol-melamine polymers appear to be effective in anchoring all types of nlmforming coating compositions to cellulosic base sheets; Coating compositions containing, as the nlm-forming constituentf'compounds such as cellulose acetate, cellulose nitrate, ethyl cellulose, methyl cellulose, deacetylated chitin, rubber, chlorinated rubber, rubber hydrochloride, cyclicized rubber, synthetic rubbers of different types, methacrylate polymers and other conventional lm-forming coating materials may be employed to coat my treated cellulosic sheets. To obtain water repellent effects, waxes such as parafiin wax, scale wax, beeswax, montan wax, carnauba wax, candelilea wax and compounds such as aluminum stearate may be incorporated in the coating composition. Plasticizers, gums, pigments, etc., may also be added thereto.

I claim:

1. A process of treating non-brous cellulosic lms which comprises the steps of impregnating a non-fibrous cellulosic iilm of regenerated ce1- lulose with an acidic, aqueous, colloidal solution containing from about 0.5% to by weight of partially polymerized melamine-formaldehyde condensation product, said product being in a state of polymerization less than that characterizing a gel, being water-dilutable, colloidal in nature, and having positively charged, hydrophilic particles of less than about one micron in diameter, washing the impregnated cellulosic film with water to remove excess melamine-formaldehyde condensation product, introducing a plasticizing agent into the cellulosic lm, drying the film and thereafter applying a water-repellent coating composition thereto.

2. A process of preparing non-fibrous, cellulosic films having a water-repellent coating anchored firmly thereto which comprises the steps of dissolving one molecular equivalent ,of a melamine-formaldehyde condensation product in an aqueous solution containing from about 0.1 to 4.0 mols of acid per mol of condensation 4product to obtain a solution having /from about 10% to 50% resin solids by Weight, allowing the solution to stand at approximately room temperature for a period of time from between about two hours to forty-eight hours until the melamine-formaldehyde condensation product has become poly-` merized to a state at which the particles thereof are hydrophilic, positively charged, less than about one micron 1n' but eine poly'- merized to a state less that characterizing a gel, adjusting the resin of said solution to e sende content or about 0.5% te 20% by weight, impregnating non-brous, cellulosic with said solution, lexcess solution from the nlm by washing with water, incorporating a plasticizing agent in the film, drying and thereafter applying a water-repellent coating compositionv thereto. s

3. A process of treating non-fibrous cellulosic films which comprises the steps of impregnating a film of regenerated cellulo with an acidic, aqueous solution containing from about 1% to 3% by weight of a hydrophilic, positively charged methylol-melamine polymer having particles lwithin the colloidal range. said solution resulting from the aging of an acidic, aqueous solution containing from about 10% to 50% by weightof methylol-rnelamine at a pH within the range of 0.5 to 4.0 until the said methylol-melamine has become hydrophilic, water-dilutable, and having positively charged colloidal particles but has not attained the state of polymerization characterizing a gel, thereafter washing the impregnated cellulosic lm with water to remove excess methylol-melamine from the surface, introducing a plasticizing agent thereinto, drying and thereafter applying a surface coating of a water-repellent material thereto.

4. A process of treating non-fibrous cellulosic films which comprises the steps of impregnating a iilm of regenerated cellulose with an acidic, aqueous solution containing from about 1% to 3% by weight of a hydrophilic, positively charged methylol-melamine partial polymer having particles within the colloidal range, said solution resulting from the aging 0f lan acidic, aqueous solution containing from about 10% to 50% by weight of methylol-melamine at a pH within the range of 0.5 to 4.0 until the said methylol-melamine has become hydrophilic, water-dilutable, and having positively charged colloidal particles but has not attained the state of polymerization characterizing a gel, thereafter washing the impregnated cellulosic iilm with water to remove excess methylol-melamine from the surface thereof, introducing a plasticizing agent thereinto, drying and thereafter applying a filmforming adhesive composition thereto.

5. A process of treating non-fibrous cellulosic iilms which comprises the steps of impregnating a lm Aof regenerated cellulose with an acidic, aqueous solution containing from about 1% to 3% by weight of a hydrophilic, positively charged methylol-melamine partial polymer having particles within the colloidal range, said solution resulting from the aging of an acidic, aqueous solution containing from about 10% to 50% by weight of methylol-melamine at a pH within the range of 0.5 to 4.0 until the said methylol-melamine has become hydrophilic, water-dilutable, and having positively charged colloidal particles but has not attained the state of polymerization characterizing a gel, thereafter washing the impregnated cellulosic iilm with water to remove excess methylol-melamine from the surface thereof, introducing a plasticizing agent thereinto, drying and thereafter applying a film-forming printing composition in discontinuous areas thereto.

6. A process of preparing non-fibrous, cellulosic lms having a water-repellent coating anchored firmly thereto which comprises the steps of dissolving one molecularequivalent of a melamineformaldehyde condensation product in an aqueous solution containing from about 0.1 to 4.0 mois of acid per mol of condensation product to obtain a solutionrhaving from about 10% to 50% -resin solids by weight, allowing the solution to stand at approximately room temperature for a period of time from between about two hours to fortyeight hours until the melamine-formaldehyde condensation product has become'polymerized to a state at which the particles thereof are hydrophilic, :positively charged, less than about one micron in diameter, but being polymerized to a state less than that characterizing a gel, adjusting the resin content of said solution to a solids content of about 0.5% to 20% by weight, impregf nating non-fibrous, cellulosic lms with said solution containing also a plasticizing agent, removing excess solution from the film, drying and v thereafter applying .7a water-repellent coating composition thereto.

7. A processof treating non-brous cellulosic films which comprises the steps of impregnating a non-ibrous cellulosic film of'regenerated cellulose with an acidic, aqueous, colloidal solution containing a plasticizing agent and from about 0.5% to 20% by weight of a partially polymerized melamine-formaldehyde condensation product, said product being in a state of polymerization less than that characterizing a gel, being waterdilutable, colloidal in nature, and having positively charged, hydrophilic particles of less thanl about one micron in diameter, removing the excess. of said impregnating solution from the surface ofthe impregnated cellulosic film, drying the lm, and thereafter applying a water-repellent coating composition thereto.

JOI-IN D. POLLARD. 

